Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses added emphasis has been placed on maximizing each given well's life and productivity over the course of the well's life. Thus, well logging, profiling and monitoring of well conditions are playing an ever increasing role in oilfield operations. Similarly, more actively interventional applications are regularly called for such as clean-out applications, opening or closing valves and sliding sleeves or any number of other maneuvers targeting maximized recovery and well life.
In addition to regular intervention for sake of monitoring and/or managing well operations, the well itself may also be of fairly sophisticated architecture. For example, in an attempt to maximize recovery from the reservoir and extend the useful life of the well, it may be of a fairly extensive depth and tortuous configuration. This may include overall depths in the tens of thousands of feet range. Once more, such wells may include extended horizontal or deviated sections of several thousand feet. As a result, interventions through such wells are becoming of ever increasing difficulty as noted below.
The above described interventions through deviated wells are generally achieved by way of coiled tubing, pipe or other suitable form of rigid or semi-rigid well access line. Thus, a logging, clean-out, shifting or other application tool may be driven through deviated well sections. Unfortunately, after a few thousand feet of conveyance through such a section, the tubing will generally begin to undergo sinusoidal buckling. This is followed by helical buckling, and soon thereafter, helical lock of the line within the deviated section such that further advancement is impossible. Of course, this is problematic where the target location for the application at hand is at a location beyond the location of the locked up, now immobile end of the coiled tubing. Further, this problem has become increasingly common given the ever increasing depths of wells and deviated well sections.
Various techniques or conveyance aids have been developed to help extend the reach of coiled tubing through such deviated sections such that the appropriate application tool may arrive at the desired target location. For example, a friction reducer may be introduced through the coiled tubing during conveyance, particularly through a deviated section. As a result, an added 10-15% or so of coiled tubing reach may be realized. In circumstances where the deviated well section is under about 3,000 feet, this may make all the difference in allowing the coiled tubing to fully traverse the section. However, as deviated well sections become longer and longer, use of a friction reducer in this manner may not be effective.
Alternatively, downhole tractoring may be used to pull the coiled tubing through the deviated well section. That is, well tractors may be attached to the coiled tubing, positioned in the well, and employed to advance downhole, pulling the coiled tubing through the well including such problematic deviated sections. Such tractoring may be fairly effective. For example, it might not be unreasonable to expect to be able to traverse as much as a 6,000 foot deviated section in this manner.
Unfortunately, while effective, the cost of tractoring is often exorbitant. In today's dollars hundreds of thousands of dollars may be spent on a dedicated tractoring conveyance application. Further, a couple of days worth of time may be lost to rig up time, not to mention the potentially added footspace requirements that may be needed at the oilfield for associated tractoring equipment. Once more, this lost time and expense assumes a successful tractoring operation. However, should a tractor fail or become stuck downhole, the added time and expense necessary to redress the issue may translate into lost hundreds of thousands if not upwards of a million dollars for the operator.
Understandably, alternatives to either tractoring or friction reducers are desirable. Accordingly, more recent attempts to help extend coiled tubing reach through deviated sections include use of vibration tools integrated with the coiled tubing. These tools may be operated at a pre-determined amplitude and frequency as an aid to extending the reach of the coiled tubing. These vibration techniques are generally considered more effective than mere introduction of a friction reducer. Once more, the cost of utilizing a vibration tool is unlikely to approach that of tractor usage.
Unfortunately, ascertaining the degree of extended reach aid afforded by a given vibration tool and technique remains a challenge. Thus, as a practical matter, the operator may be left largely blind guessing to use vibration assistance only to become stuck before reaching the target depth and thus have to retry with a different set of vibration parameters or even worse to completely retry with a new tractoring application. Where the latter is the case, the exorbitant cost of extending reach via tractor has now only been further increased.